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    SubjectRE: [PATCH-v2 1/2] mpt3sas: Refcount sas_device objects and fix unsafe list usage
    From: Sreekanth Reddy [mailto:sreekanth.reddy@avagotech.com]
    Sent: Tuesday, September 08, 2015 5:26 PM
    To: Nicholas A. Bellinger
    Cc: linux-scsi; linux-kernel; James Bottomley; Calvin Owens; Christoph
    Hellwig; MPT-FusionLinux.pdl; kernel-team; Nicholas Bellinger; Chaitra
    Basappa
    Subject: Re: [PATCH-v2 1/2] mpt3sas: Refcount sas_device objects and fix
    unsafe list usage

    On Sun, Aug 30, 2015 at 1:24 PM, Nicholas A. Bellinger <nab@daterainc.com>
    wrote:
    > From: Nicholas Bellinger <nab@linux-iscsi.org>
    >
    > These objects can be referenced concurrently throughout the driver, we
    > need a way to make sure threads can't delete them out from under each
    > other. This patch adds the refcount, and refactors the code to use it.
    >
    > Additionally, we cannot iterate over the sas_device_list without
    > holding the lock, or we risk corrupting random memory if items are
    > added or deleted as we iterate. This patch refactors
    > _scsih_probe_sas() to use the sas_device_list in a safe way.
    >
    > This patch is a port of Calvin's PATCH-v4 for mpt2sas code, atop
    > mpt3sas changes in scsi.git/for-next.
    >
    > Cc: Calvin Owens <calvinowens@fb.com>
    > Cc: Christoph Hellwig <hch@infradead.org>
    > Cc: Sreekanth Reddy <sreekanth.reddy@avagotech.com>
    > Cc: MPT-FusionLinux.pdl <MPT-FusionLinux.pdl@avagotech.com>
    > Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
    > ---
    > drivers/scsi/mpt3sas/mpt3sas_base.h | 25 +-
    > drivers/scsi/mpt3sas/mpt3sas_scsih.c | 479
    > +++++++++++++++++++++----------
    > drivers/scsi/mpt3sas/mpt3sas_transport.c | 18 +-
    > 3 files changed, 364 insertions(+), 158 deletions(-)
    >
    > @@ -2763,7 +2874,7 @@ _scsih_block_io_device(struct MPT3SAS_ADAPTER *ioc,
    > u16 handle)
    > struct scsi_device *sdev;
    > struct _sas_device *sas_device;
    >

    [Sreekanth] Here sas_device_lock spin lock needs to be acquired before
    calling
    __mpt3sas_get_sdev_by_addr() function.

    [Chaitra]Here instead of calling " __mpt3sas_get_sdev_by_handle()" function
    calling
    "mpt3sas_get_sdev_by_handle()" function will fixes "invalid page access"
    type of kernel panic

    > - sas_device = _scsih_sas_device_find_by_handle(ioc, handle);
    > + sas_device = __mpt3sas_get_sdev_by_handle(ioc, handle);
    > if (!sas_device)
    > return;
    >
    > @@ -2779,6 +2890,8 @@ _scsih_block_io_device(struct MPT3SAS_ADAPTER *ioc,
    > u16 handle)
    > continue;
    > _scsih_internal_device_block(sdev, sas_device_priv_data);
    > }
    > +
    > + sas_device_put(sas_device);
    > }
    >


    Regards,
    Chaitra


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